1. Field of the Invention
The present invention relates to a mechanical supercharger, and more particularly to a mechanical supercharger for supercharging an engine for automobiles and so on.
2. Description of the Prior Art
A conventional mechanical supercharger is disclosed, for example, in Japanese utility model application laid-open publication No. 2(1990)-34728. As shown in FIG. 8, this conventional mechanical supercharger 80 includes four shafts 82, 83, 89, 90 rotatably supported on a housing 81, rotors 84, 85 disposed on the about center portion of the shafts 82, 83, respectively and timing gears 86, 87 disposed on one end of the shafts 82, 83 respectively so that both shafts 82, 83 are synchronously rotated. In this mechanical supercharger 80, a variable speed mechanism 88 is disposed between the shafts 89, 83. Thereby, the rotation of the shaft 89 is increased and is transmitted to the shaft 83. Similarly, a variable speed mechanism 91 is disposed between the shafts 90, 83. Thereby, the rotation of the shaft 90 is increased and is transmitted to the shaft 83. Now, the variable ratio of the variable speed mechanism 88 differs from the variable speed ratio of the variable speed mechanism 91. Furthermore, in this mechanical supercharger 80, pulleys 94, 95 are installed on end portions of the shafts 89, 90 through electromagnetic clutches 92, 93, respectively. These pulleys 94, 95 are driven by a driving source such as an engine (not shown) and so on through a belt (not shown) and the operational condition of the electromagnetic clutches 92, 93 are controlled by a control device 96.
In this conventional mechanical supercharger 80, either of the electromagnetic clutches 92, 93 is selectively connected by the control device 96 and the rotors 84, 85 are driven in accordance with the variable speed ratio of either of the variable speed mechanisms 88, 91. Thereby, the supercharging pressure of the mechanical supercharger 80 is changed.
In the above conventional mechanical supercharger 80, however, since two expensive electromagnetic clutches are employed and furthermore two variable speed mechanisms are employed, the cost and the weight of the mechanical supercharger increase remarkably.
Furthermore, when either of the electromagnetic clutches 92, 93 is connected, the shafts 82, 83, 89, 90 and all of rotational members (each gear and so on) which are disposed on the shafts 82, 83, 89, 90 are driven. When the electromagnetic clutch 92 is connected, for example, it is not necessary to rotate a rotation group of the shaft 90. Nevertheless, the rotation group of the shaft 90 is rotated. Accordingly, the rotating mass of the rotation groups which are rotated for supercharging increases and therefore the response of the mechanical supercharger deteriorates.